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Topic Review (Newest First)

08-06-2012 03:53 PM

oldbogie

Quote:

Originally Posted by PatM

68 NovaSS and BigDog7373
Thanks for enlightening me. When I bought my parts (back 10-12 years ago) the market was more limited, and the vast majority of internal balanced 383 Stroker cranks required the 6.0 rods. This was for the reason that CNC Northeast mentioned, or at least I thought and continue to believe. The Mallory Metal is, of course, an answer for almost anything remotely within reason. But, it is very expensive. And the more you need, the more expensive it becomes. As a result of your posts I went to the Eagle and Scat sites and found a broad assortment of cranks and kits set up for internal balance with 5.7 rods. I have to presume this requires the use of their specified (or somewhat akin) pistons, to clear the counterweights.

Anyway, again, thanks for enlightening me . . And CNC Northeast -- I still agree that for an internally balanced 383 it probably makes most sense to use 6 inch rods . . but it seems there are ways to use those 5.7 inch rods now in an internally balanced 383, without the need for Mallory Metal. I'm sure you knew that already, but I (for one) feel enlightened.

PatM

You are right; this is a place where you need to pay attention to the crankshaft manufacturer's recommendations as to rods and pistons. After-all the counterweight is there to offset a complex sum of weights and partial weights of the material hanging on the rod throw portion of the crank. This is divided into rotation and reciprocating weights.

The crankshaft rod throws are rotating weights to these are added the weight of the big end of the connecting rods. So the big ends need to be made to weigh equally. One can see that the rod throws are not equaled and will contribute to some degree of off balance of any one compared to the others when the crank is spun.

The connecting rods not only need to the big ends of equal weight but the entire rod also has to be of identical weight of any one to all others, this usually means adjusting the small end after the big ends have been equaled. This would include the weight of typical rod bearing set. The total weight of the rod along with equaling the weight of the pistons each to all others plus a ring set are added together where in the case of a 90 degree V8 one half of the sum of the connecting rod and piston weights and all of the weight of the big end are summed, This result becomes the bob-weight that is attached to the crankshaft for the spin balance cycle.

Given there is only so much mass that can be stuffed into a counterweight because of space limitations to clear the piston at BDC and the crankcase, if the use of Mallory Metals is to be avoided one needs to be cautious about part weight selection.

I use the term Mallory Metal somewhat loosely as simply meaning heavy metals rather than Mallory as manufacturer and seller of heavy metal alloys. These alloys contain large amounts of metals like tungsten which weigh about twice that of steel or cast iron and are rather expensive so you don't want to create a situation where you have to use much of this stuff. There are plenty of pictures on the web and in the popular press of huge multiple applications of Mallory metals in some poor crankshaft where the situation has gone wrong for improper parts selection among other things that can happen of huge multiple applications of Mallory metals.

Always try to use a crank that has the all of rod throws drilled. This saves a lot weight in the rod throw making these cranks a lot easier to balance.

Bogie

08-06-2012 03:44 PM

PatM

lmsport
Yeah, so true. My machinist/balancer had to remove a lot of material from the counterweights because of the very light (Lunati Streetrace, no longer available, I think) rods, pistons and pins that I selected. His comment after completing the balance was the the engine should be a "zinger", meaning quick to build up revs. . . . . I hadn't mentioned it to him, but that was exactly what the goal was. Now that I think of it, when I gave him the crankshaft and the value for the bobweights, I don't think he believed me. He asked me to bring in the parts. So I brought in one piston, one pin, spirolocks, one rod, one bearing and a ring set, all previously static balanced. I don't recall the exact bobweight (I think 1668, but I can't swear) but his calcs came out within 1 gm of the value I had given him.

Pat

08-06-2012 03:16 PM

lmsport

There can be a big difference in weight between different rods and pistons, too. Lighter parts make it easier to balance with smaller counterweights.

08-06-2012 02:53 PM

PatM

68 NovaSS and BigDog7373
Thanks for enlightening me. When I bought my parts (back 10-12 years ago) the market was more limited, and the vast majority of internal balanced 383 Stroker cranks required the 6.0 rods. This was for the reason that CNC Northeast mentioned, or at least I thought and continue to believe. The Mallory Metal is, of course, an answer for almost anything remotely within reason. But, it is very expensive. And the more you need, the more expensive it becomes. As a result of your posts I went to the Eagle and Scat sites and found a broad assortment of cranks and kits set up for internal balance with 5.7 rods. I have to presume this requires the use of their specified (or somewhat akin) pistons, to clear the counterweights.

Anyway, again, thanks for enlightening me . . And CNC Northeast -- I still agree that for an internally balanced 383 it probably makes most sense to use 6 inch rods . . but it seems there are ways to use those 5.7 inch rods now in an internally balanced 383, without the need for Mallory Metal. I'm sure you knew that already, but I (for one) feel enlightened.

PatM

08-06-2012 12:24 PM

oldbogie

Quote:

Originally Posted by 2old2fast

Bogie , Sorry , but all aftermarket are not external/external ! Strokermotors lists 3 different scenario's- Int/Int-Int/Ext - Ext/Ext. Most,but not all 6" rod listings are Int. Most , but not all 5.7" rod listings are int..

dave

Dave, I believe I used the term "that use external balance" the remainder being. "use the 400 balancer". I was not intending to discuss the effects of 6 inch rods versus 5.7 and their effect on crank balance only to clarify that the external balance 383 stroker crank is intended to use, or at least start from, the 400 damper and flywheel or flexplate.

An internal balanced 383 stroker will use the neutral balanced 350 damper and flywheel/flexplate as the best starting point. This will hold true whether the crank began life as an internally balanced with 6 inch rods or and externally balanced with 5.7 inch rods that is forced by the use of Mallory Metal to become an internally balanced crank. Which is to say that the choice of external or internal balanced damper and flywheel/flexplate needs to match the choice of external or internal balance crank.

I am not a big fan of externally balanced engines, while the crankshaft as a whole rotates on center just as it does when internally balanced; there remains a long distance between out-of-plane forces which results in bending moments along the crankshaft. Evidence of these can be seen in the main bearings when the engine is opened up you will typically see bearing shells that exhibit inconsistent wear both within the diameter and across the width. Given that the engine builder needs to understand how much of this is flexing of the crankshaft between bearing bays and how much is lack of alignment through the bearing bores.

Internal balancing eases this situation somewhat but doesn't entirely make it go away. Crankshafts do funny things which is one reason why there is so much counterweight on the ends compared to the inboard throws. Some if this is simply space related where the inboard throws don't have enough space for full counterbalance and some is the tendency of the crank to want to orbit its ends instead of just rotate them on a center. So the big counterweights are king of pulling the ends back to the plane of rotation. The center two throws usually don't have counterweights as all but depend upon their masses in opposition to achieve balance. The problem with this is that there is a lever arm distance between these throws that results is the loads being offset by that distance, this then wants to bend the crank between the number two and four main with number three being a pivot point. This is the reason why 4 bolt and cross bolted mains are found in the middle of high performance blocks. This condition can be relieved by the use of counter weights on the inboard side of throws two and three. But for a street engine this adds cost where it typically isn't necessary although the old Ford Y block crank was weighted here. The extra weight slows crankshaft acceleration so it's usually isnít found on drag race engines. It is rather commonly found on NASCAR cup engines where constant high loading on the crank requires better bearing bay to bay balance for reduced wear on bearings and less concentrated loading into the block at this point combined with a reduced need for absolute maximum rates of crankshaft acceleration as found in drag engines. There are of course exceptions where some builders feel the aftermarket competition block and crankshaft are sufficiently strong enough to sustain these loads for the needed periods of time and they want the lighter faster to accelerate crankshaft that is more akin to what the drag racers would use.

Bogie

08-04-2012 10:30 AM

2old2fast

Bogie , Sorry , but all aftermarket are not external/external ! Strokermotors lists 3 different scenario's- Int/Int-Int/Ext - Ext/Ext. Most,but not all 6" rod listings are Int. Most , but not all 5.7" rod listings are int..

dave

08-04-2012 06:05 AM

CNC BLOCKS NE

Quote:

Originally Posted by 68NovaSS

I have a 3.750 stroke aftermarket crank in my 383 blower car, with 5.7 rods, and it's internally balanced, it can go either way, no question about that. I'll assume from your post, an OEM 400 crank doesn't lend itself to internally balancing.

I have internally balanced 400 cranks its very costly but it was for a cheater circle track engine.

I have seen a few 5.7 rod cranks that will internally balance but most seem to be internally.

All the strokers I build I use 6 inch rods better rod ratio, less piston hanging out of the borre at BDC, liter piston, internally balance.

08-03-2012 05:49 PM

68NovaSS

Quote:

Originally Posted by CNC BLOCKS NE

I think the OP is talking about a 3.750 stroke not a 3.480 stroke big differance between the two.

I have a 3.750 stroke aftermarket crank in my 383 blower car, with 5.7 rods, and it's internally balanced, it can go either way, no question about that. I'll assume from your post, an OEM 400 crank doesn't lend itself to internally balancing.

08-03-2012 05:33 PM

CNC BLOCKS NE

Quote:

Originally Posted by 68NovaSS

I understand that, what I was referring to was using a 5.7/6.0 rod on an aftermarket stroked crank, say 383, using the appropriate pin height pistons. The poster didn't mention using a particular crank, be it OEM or aftermarket, just the rod being used.

What I don't understand is why you say a 5.7 rod crank is usually externally balanced, case in point, a stock, internally balanced 350 Chevy uses a 5.7 rod.

I think the OP is talking about a 3.750 stroke not a 3.480 stroke big differance between the two.

08-03-2012 02:01 PM

oldbogie

Quote:

Originally Posted by zildjian4life218

Awesome reply! He has an aftermarket cast crank that is externally balanced. So does he need the 400 harmonic balancer along with the flexplate?

Yes!

The aftermarket 383 stroker cranks that use external balance are made to also use the 400's damper up front and flywheel or flexplate at the rear.

Bogie

08-03-2012 01:13 PM

Mr. P-Body

I've never seen any correlation between rod length and "type" of balancing. The application usually determines the type.

The flexplate or flywheel AND the balancer MUST be physically attached to the crankshaft during the process if "external". It's not uncommon to spin a crankshaft without the balancer and flexplate/flywheel if "internal". The balancer and flexplate/flywheel can be "spun" independently and checked for "zero".

Jim

08-03-2012 12:13 PM

68NovaSS

Quote:

Originally Posted by CNC BLOCKS NE

OHHHHH yes it does as the 5.7 rod crank uses shorter counter weights and in most cases they are extrernally balanced.

A 6 inch rod crank uses bigger or taller counter weights and can be internally balanced.

Thats why all OEM 400's with their short rods are externally balanced.

I understand that, what I was referring to was using a 5.7/6.0 rod on an aftermarket stroked crank, say 383, using the appropriate pin height pistons. The poster didn't mention using a particular crank, be it OEM or aftermarket, just the rod being used.

What I don't understand is why you say a 5.7 rod crank is usually externally balanced, case in point, a stock, internally balanced 350 Chevy uses a 5.7 rod.

08-03-2012 09:43 AM

bigdog7373

Quote:

Originally Posted by zildjian4life218

Awesome reply! He has an aftermarket cast crank that is externally balanced. So does he need the 400 harmonic balancer along with the flexplate?

Yes 400 flex plate and balancer. This has been said multiple times.

08-03-2012 09:16 AM

2old2fast

Best reply I can give is ---check w/ the manufacturer..

dave

08-03-2012 08:54 AM

zildjian4life218

Quote:

Originally Posted by Mr. P-Body

Most aftermarket forgings ARE "internal". Most castings are not. All of them can be "converted" using Mallory Metal (tungsten) as stated. Not cheap to "convert".

Many shops with a balancer have "on hand", stock 400 balancer and flexplate. We have a Pontiac flexplate that "lives" at the balance shop for this purpose.

The "bolt on" weight is popular among the 383 "crowd" because it allows the use of the "zero" flexplate or flywheel (they usually already have a 350 piece).

The clutch "cover" (pressure plate) is often attached during balancing for manual transmissions. Not used in automatic applications. With modern manufacturing techniques, this has become less an issue than it was 20 years ago.

Lastly, some "myths" about balancing. SAE "standards" are that the rotating assembly is balanced to within 1/2 of 1% of the total rotating "mass". In a 383, that amounts to about 28 grams. Most balance shops routinely balance to within 1 gram, FAR exceeding standards. The slight variations from using different "stock" balancers and flexplates/flywheels are not significant.

For higher revving engines (over 6,500), often "over-balance" is included. That's where the factor for the bob weight is changed from 50% (reciprocating) to a little higher percentage to offset the downward "thrust" under hard accelleration (engine speed, not car speed). High-end "big" engines usually have an over-balance of 4-5%.

FWIW

Jim

Awesome reply! He has an aftermarket cast crank that is externally balanced. So does he need the 400 harmonic balancer along with the flexplate?

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